By any chance are any of you on Windows? It appears that the zip capabilities built into Windows has problems with unzipping.
I discovered this after comparing the contents of the following directory with the contents of the zip file:
wp-includes/js/tinymce
My installation has fewer files in the above directory than than the zip file contains. My guess is that Windows has problems with the wp-tinymce.js.gz file.
Once I replaced the missing files, my install started working again.
